Refrigeration inventory control

ABSTRACT

An apparatus and process for controlling refrigeration in a closed cycle. An inventory recorder and controller in communication with major holdup locations in the refrigeration circuit determines the amount of the refrigerant in the system. The amount is measured, recorded and maintained by means responsive to the difference between a set value and the value measured by the inventory recorder and controller. The apparatus and method is applicable to a multicomponent refrigerant where individual control is maintained over each component.

lJnited States Patent Sarsten et all.

[451 June 13, 1972 REFRIGERATION INVENTORY CONTROL Jan A. Sarsten,Millington, N.J.; Kenneth I. Zacks, Oxshott, England; Michael C. Myers,Tripoli, Libya Esso Research and Engineering Company April 29, 1970 [72]Inventors:

Assignee:

Filed:

Appl. No.:

[52] U.S. Cl ..62/77, 62/114, 62/149,

62/292, 137/90, 137/93 Int. Cl ..F25b 45/00 Field of Search 2/77, 85,114, 149, 242, 529;

[56] References Cited UNITED STATES PATENTS 3,400,552 9/1968 Johnsonetal. ..62/149 9/ l 960 Etherington ..62/ 149 5/1970 Becker PrimaryEvaminer-William F. O'Dea Assistant Examiner-P. D. FergusonAttorney-Manahan and Wright and Donald F. Wohlers [57] ABSTRACT Anapparatus and process for controlling refrigeration in a closed cycle.An inventory recorder and controller in communication with majorholduplocations in the refrigeration circuit determines the amount of therefrigerant in the system. The amount is measured, recorded andmaintained by means responsive to the difference between a set value andthe value measured by the inventory recorder and controller. Theupparatus and method is applicable to a multicomponent refrigerant whereindividual control is maintained over each component.

16 Claims, 2 Drawing Figures PATENTEDJUH 13 I972 SHEET 10F 2 AttorneyJanASarsfen Inventors Kenn efh Zac/rs M/chae/ C. Myers MW I PATENTEDJUH13 m2 SHEU 2 BF 2 V: mv MGM m D G ww F mm vw QM Qw n km 3 mm mm R R & wwQ Q mm mm Jon/1. Sara/en Inventors Kennel/7 Zac/rs Michael C. Myers W EAttorney 1 REFRIGERATION INVENTORY CONTROL BACKGROUND OF THE DISCLOSUREThis invention is directed to an apparatus and process for controllingrefrigeration of a closed cycle. More specifically, this invention isdirected to an apparatus and process for controlling a multicomponentrefrigeration cycle. Still more specifically, this invention is directedto an apparatus and method for measuring, recording and controlling theinventory of the gaseous phase of a multi-component refrigerant so as tomaintain a constant inventory of refrigerant in the refrigerationcircuit.

A major problem, in the prior art, relating to closed cyclerefrigeration processes has been the problem of refrigeration makeup dueto losses in the system. Such losses must be made up by additionalrefrigerant. However, problems arose in complex refrigeration circuitsin determining whether refrigerant had been lost and how much,particularly when the load on the refrigeration cycle changed. At thosetimes, it was often impossible for an operator to determine whetherchanged conditions indicated refrigerant losses, or whether such changeswere due to changes in loading conditions. This problem was inherent inthe prior art methods for control of refrigeration makeup. In the priorart, refrigeration makeup was usually determined as a function ofcompressor suction or discharge pressure. These systems workedreasonably well in those cases where the measured variable could bereliably predicted for any change in conditions. However, in complexrefrigeration cycles where variable speed centrifugal compressors areemployed in refrigeration cycles using multiple refrigeration stages andmulticomponent refrigerants, such predictions are difficult to make andnot very reliable. In such systems, changes in compressor speed, flowrate and refrigeration load cause changes to the pressure in the systemand it is not possible to know to what extent the accompanying continualloss of refrigerant (or gain) was responsible.

This argument can be illustrated by the typical situation where anincreased load is imposed on a closed cycle system using a centrifugalcompressor. The speed of the compressor is increased. This results in agreater pressure difference across the compressor and/or a greaterrefrigerant flow rate. This would cause the suction pressure to decreaseand the discharge pressure to increase. However, the operator cannot besure whether some of the resultant decreased suction pressure isattributable to increased refrigerant losses. To compensate for hisuncertainty, the operator would bring refrigerant makeup into the systemuntil the suction pressure was brought up to the level existing prior tothe change in loading conditions. With suction pressure restored at thenow higher compressor speed, discharge pressure would increase evenmore.

This typical situation results in the design of compressors that mustaccommodate a wider range of pressures than would have been the case ifthe suction pressure were allowed to stay at the pressure attained withchange in speed.

In the typical situation where a decreased load is imposed on a closedcycle system using a centrifugal compressor, the speed of the compressorwould be decreased. This would cause the suction pressure to increaseand the discharge pressure to decrease. To compensate for uncertaintiesin the system inventory, the operator would decrease the suctionpressure by venting refrigerant.

These situations result in the need for larger refrigerant storagefacilities and larger refrigerant makeup facilities than would benecessary in the case where inventory can be measured, recorded andcontrolled to fit system losses independent of changing processingconditions.

BRIEF SUMMARY OF THE INVENTION The apparatus and process of the instantinvention is designed to overcome the problems described above. Theinstant invention is directed to an apparatus and method wherein theamount of refrigerant in a refrigeration cycle is continually measured,recorded, and controlled so as to maintain a constant inventory ofrefrigerant. In this way refrigeration compressor costs are reduced dueto easier system utilization of the entire performance range of thecompressor; heat transfer and piping equipment costs are reduced as aresult of lower pressure ratings for the same refrigerationrequirements; refrigerant makeup facility costs are reduced as a resultof a smaller makeup facility; and operating costs are reduced as aresult of decreased refrigerant consumption and/or refrigerant standbystorage. In accordance with the instant invention, an apparatus andmethod is provided for controlling refrigerant inventory in arefrigeration cycle in which the temperature and pressure of therefrigerant is sensed at major holdup locations in the cycle where therefrigerant is in the gaseous phase, as well as the percentagecomposition of each component of the refrigerant if it is amulticomponent refrigerant. This data is transmitted to a computer. Thecomputer calculates the total amount of each component of therefrigerant present in the system and means responsive to the computeroutput are provided to adjust the amount of each component brought intothe system so that the refrigerant inventory in the circuit remainsconstant.

BRIEF DESCRIPTION OF THE DRAWINGS The invention may be better understoodby reference to the accompanying drawings of which:

FIG. 1 is a schematic diagram of the logic of the inventory recordercontroller of the instant invention;

FIG. 2 is a schematic flow diagram of the instant invention.

DETAILED DESCRIPTION The apparatus and method of the instant inventionhas at its central core a computer comprising an inventory recorder andcontroller. FIG. 1 is an illustration of the logic upon which thecomputer operates. In order to better understand this logic, a review ofthe pertinent thermodynamic relationship is required. The number ofmoles of a gas in a constant volume system is characterized by N PV/ZRT1 where N is the number of moles of gas, P is pressure, V is volume, 2is compressibility factor, R is gas law constant, and Tis thetemperature.

It is understood that the compressibility factor Z varies with changesin temperature and pressure. However, the compressibility factor, whichadjusts the ideal equation of state for non-ideal gases is taken as aconstant for the particular gas, at the particular sensing location,involved. This introduces only minute errors since this factor is takenat the average value, at the particular sensing location, overanticipated conditions. It should further be appreciated that a varyingcompressibility factor as a function of the temperature and pressure caneasily be built into the computers logic circuit.

Since the volume, compressibility factor and the gas law constant areall constants, at the particular sensing location, the equation abovecan be simplified as N K (P/ T) (2) where K V/ZR (3 Another relationshiprelates the total number of moles in a system to the sum of theindividual number of moles, of each component, at each sensing locationin the system. Thus,

N N N, Total Moles Substituting equation (2) into equation (4) yields K,(P,/T,) K, (P /T K (P,,/T,,) Total Moles(5) Turning now to FIG. 1 whichdepicts the computer logic for a system comprising n sensing locations,the computer is fed temperature and pressure data from the n sensinglocations in the system. This data is operated upon in Blocks 10, 10aand 10b wherein the pressure is divided by the temperature to give avalve of P./ T. This data is then sent to Block 1 1, 11a and 1 lb. InBlock 11, 11a and 11b, the P/Tvalue is multiplied by K. The value K hasbeen defined in Equation 3 above as equal to V/ZR. Of course, K isdifferent for each sensing location due to the different effectivevolume and compressibility of each sensing location. Each one of thesevalues represents the total number of moles of the individual componentspresent in the refrigerant mixture at that sensing location. In Block12, 12a and 1212, the individual number of moles of each component ineach sensing location is determined by multiplying the value K(P/T) thatenters Block 12, 12a and 12b by the percentage composition of eachcomponent at that sensing location as determined by a chromatographmonitoring that location.

Thus, assuming a three component mixture, in a three sensing locationfacility, the output of Block 12, 12a and 12b i (x) (K) P/T, (y) (K) P/Tand (z) (K) P/T where x, y and 7, represent the mole fraction of thethree components present in the refrigerant. Thus .r,K, (P /T representsthe number of moles of x in sensing location 1; y K (P /T represents thenumber of moles of y in location 2 etc. It should be appreciated that ifthe refrigerant were a single component Block 12 would not be present inthe computer logic.

The total moles of each component in each sensing location is nowcombined in Block 13. This yields the total number of moles of eachcomponent of the refrigerant in the gaseous phase in the refrigerationcircuit. To this sum is added the known or measured amount ofrefrigerant present in the liquid phase as will be describedhereinafter. This sum is broken down by component, so that the resultsof Block 13 is the total number of moles of each refrigerant componentpresent in the system. This result is one of the outputs of thecomputer. In addition, these results are inputed to Block 14 where theyare totalled to yield the total number of moles in the system, which isanother output of the computer. It should be appreciated that the outputmay be converted in mass units by multiplying each component by thatcomponents molecular weight.

FIG. 2 is a flow diagram of the instant invention. In FIG. 2 a typicalclosed cycle refrigeration unit generally designated is illustrated. Itincludes a refrigeration compressor 22. Although for convenience asingle stage compressor is illustrated, the instant invention is notlimited to a single stage compressor, thus two or more compressor stagesmay be substituted. The inlet end in communication with the compressor22, more typically called the suction side, is designated at 32. Throughconduit 32 flows the low pressure gas on its way to the compressor 22.The gas is compressed in the refrigeration compressor 22 and isdischarged through conduit 34, which communicates with said compressor22. Conduit 34 represents the discharge end or outlet of the compressor.The gas flowing through conduit 34 is cooled and at least partiallycondensed, in a heat exchanger 45. The pressurized fluid flows into alow pressure holdup volume 26 by way of a conduit 61.

In the preferred embodiment illustrated in FIG. 2, the low pressureholdup volume 24 is disposed upstream of the inlet or suction conduit32. In a preferred embodiment, pressure and temperature sensorsdesignated 28 are in communication with said volume 24. The temperatureand pressure sensors 28 in FIG. 2 may utilize any convenient measurementmeans such as thermocouples and pressure transducers respectively. Thesensors 28 are in communication with an inventory controller andrecorder 21 by means of transmission means 31. In the preferredembodiment illustrated in FIG. 2, transmission means 31 compriseselectronic conduits. Alternatively the transmission means 31 maycomprise pneumatic conduits. In addition to the temperature and pressuresensors 28, a chromatograph 29, is in communication with the volume 24.Thus, the gas in tank 24 is analyzed in the chromatograph 29 todetermine the composition of the multicomponent refrigerant therein. Itshould be appreciated that if a single component refrigerant wereemployed, there would be no need for the chromatograph 29 and it wouldnot be included in the apparatus of the instant invention. In the caseof a multicomponent refrigerant, chromatograph 29 provides a compositionbreakdown of the components of the refrigerant. This percentagecomposition data is provided to the inventory recorder and controller 21by means of transmission means 33. In the preferred embodiment shown,transmission means 33 is an electronic conduit.

The inventory recorder and controller 21 comprises a computer connectedto recording means and control means. It should be appreciated thatalthough it is preferred to have both a recording means as well as acontrol means in communication with the computer, it is possible toemploy the computer of the instant invention with only one of thesemeans, in which case the system is limited to inventory recording orinventory automatic control. Any of the standard computers may beemployed as part of the recorder/controller 21. Thus, an electronicanalog computer, a pneumatic analog computer, a direct digital computer,or much simplified versions thereof may be employed. No matter whichkind of computer is utilized, the logic illustrated in FIG. 1 isprogramed therein resulting in a total mole or mass output as well as anindividual component molar or mass outputs.

Calculated outputs are transmitted by electrical conduit 35 to arecorder 39 which prints out these results. The recorder/controller 21is also in electrical communication, by means of a pair of conduits 41and 43, with a pair of control valves 36 and 38, respectively. Thesevalves control addition and subtraction of refrigerant, respectively,into the system. Control valve 36 is disposed at point along the lengthof a conduit 30. Conduit 30 provides communication between a makeupfacility 50 and the low pressure holdup volume 24. Although FIG. 2 showsa single facility 50, it should be appreciated that in the case of amulticomponent refrigerant, a number of makeup facilities 50 equal tothe number of refrigerant components would be provided. Obviously, therewould be also an equivalent number of conduits communicating between themakeup facilities and the low pressure holdup volume 24 as well ascontrol valves of the type illustrated at 36. It should be understoodthat the control valve or valves 36 are responsive to a signal generatedby the controller 21 and communicated to said valves 36 by means ofelectrical conduits 41. It should further be understood that the makeupcontrol is on an individual component basis. Similarly, there may be aplurality of outlet control valves 38 though only one is shown forsimplicity. Valve 38 is also responsive to the controller 21 by means ofelectrical conduit 43. Control valve 38 is disposed along the length ofa conduit 37 which communicates between the low pressure holdup volume24 and a location outside the closed cycle 40. It should be appreciatedthat the subtraction connection to volume 24 is illustrative and in noway limits the location or locations of such subtraction lines. Thelocation of the subtraction lines is dictated by considerations relatingto percentage composition of the stream at a particular location as willbe described in greater detail hereinafter. Obviously, ifa singlecomponent refrigerant is employed only a single exhaust subtraction lineis used and it may be connected to any convenient point in the system.The location 40 outside the system in a preferred embodiment is a flare.That is, in those cases where the refrigerant is combustible it isburned. In those cases where the refrigerant is not a combustiblemixture or where the refrigerant is to be stored, other suitable meansto dispose of the refrigerant are provided. Normally, the control modeof the refrigeration cycle would be such that venting or subtraction ofrefrigerant is minimized for obvious reasons.

Returning now to the closed cycle 20, the discharge end of thecompressor 22 is in communication with a high pressure holdup volume 26by means of a conduit 34. Again holdup volume 26 is monitored by sensorsindicated at 60 which sense temperature, pressure and composition of thestream at that location. It should be appreciated that single measuringand single transmission conduit symbols, 60 and 62, respectively, areused for convenience. Obviously, separate measuring instruments areemployed and each instrument is separately connected to the computer ofthe inventory recorder and controller 21. In preferred embodimentsthermocouples, pressure transducers and chromatographs are respectivelyemployed to determine these properties. The temperature, pressure andcomposition values are signaled to the recorder-controller 21 byelectrical conduits 62.

Thus, the inventory recorder and controller 21 of the instant inventionreceives signals from those particular sensing locations in the cyclewhere the bulk of the gaseous refrigerant is stored and accumulated. Itshould be appreciated that in a typical discharge high pressure holdupvolume of the kind illustrated at 26 in FIG. 2, the refrigerant fluid,if multicomponent, is a two-phase mixture. In the preferred embodimentcontemplated by the embodiment illustrated in FIG. 2 such is the case.In that case, the level of liquid is controlled (not shown). Thecomputer of the inventory recorder and controller 21 is programmed toaccount for the moles of liquid in the fixed volume set by the levelcontroller so that the total inventory of refrigerant is accounted for.Furthermore, the computer can be programmed by the use of well knownsolution and chemical thermodynamic relationships to determine the exactcomposition of the liquid phase whose volume is predetermined by thelevel controller. This is calculated from the data already known, thatis, temperature, pressure, and composition of the gaseous phase combinedwith the knowledge that the liquid and gaseous phase are in equilibrium.If the liquid level is not controlled at a fixed level but allowed tofluctuate for other process reasons, the level could be measured and theoutput of the measurement sent to the computer of thecontroller-recorder 21 for liquid component calculation.

It should further be appreciated that although the embodimentillustrated in FIG. 2 only shows two holdup volumes, in more complexrefrigeration cycles, there are additional holdup volumes in proportionto the number of stages of compression and/or stages of refrigeration.It should be obvious that any additional volumes employed in morecomplex systems would be similarly monitored and controlled by theinventory controller.

Obviously, the instant invention is not directed to precise but ratherapproximate refrigeration monitoring which is all that is required formost practical applications. The selection of a finite rather thaninfinite number of sensing locations, and the use of average propertiesat each of the sensing locations, results in an inventory controllerthat is accurate within :5 percent in a typical practical application.Thus, precision is more than that required to adequately control changesin refrigerant inventory.

The remainder of the closed cycle 20, that is the cycle between the highpressure discharge holdup volume 26 and the low pressure suction holdupvolume 24 is illustrative of a simple refrigeration system. Thus, theembodiment illustrated in FIG. 2 should not be considered limiting butis rather a minimum type of cycle.

In the instant embodiment, a first refrigerant stream flows in a conduit42 which communicates between the liquid phase of the refrigerantcontained in the discharge holdup volume 26 and a flash valve 44. Theliquid refrigerant is flashed adiabatically across the valve 44. Thecold refrigerant next enters a heat exchanger 50 by way of a conduit 46which communicates between flash valve 44 and the heat exchange 50. Therefrigerant is heated while cooling a stream generally indicated at 52in the heat exchanger 50. The stream 52 represents the load thatrefrigeration cycle is designed to cool. The heated and now gaseousrefrigerant stream flows from the exchanger 50 back into the suctionholdup volume 24 by means ofa conduit 48.

A second refrigerant stream flows in a second conduit 53 incommunication with the volume 26. Conduit 53 directs the vapor phase ofthe refrigerant contained in the discharge holdup volume 26 to a heatexchanger 54. In exchanger 54 the vapor phase refrigerant stream iscooled and partially condensed by a portion of the flashed refrigerantstream flowing in conduit 46. The cooled stream exiting the heatexchanger 54 enters a conduit 60 which directs the stream to a flashvalve 55. The two-phase stream is flashed adiabatically across valve 55.The flashed refrigerant flows out of the valve through a conduit 56 toanother heat exchanger 57. The flashed stream is heated in exchanger 57while further cooling the load stream 52. The heat refrigerant stream isthen remixed with the first refrigerant stream in conduit 46 by way of aconduit 62 which communicates between the heat exchanger 57 and conduit46. A fraction of two refrigeration streams in conduit 46 is bypassedthrough a conduit 64 to provide the cooling stream in heat exchanger 54.This stream is heated therein exiting through a conduit 66. Conduit 66directs the heated refrigeration stream back to the remainder of therefrigeration stream in conduit 48. The combined stream then entersvolume 24 by way of said conduit 48.

In operation, the computer of the inventory recorder and controller 21is programmed as previously described (see FIG. 1). One additional inputinto the computer program could be the desired set values for the amountof each component of refrigerant in the system. This input is omitted inthe special case where the computer is used only in conjunction with arecorder as will be obvious from the following description.

Operation of the cycle 20 begins with the startup of the compressor 22.The temperature and pressure and if a multicomponent refrigerant isused, the composition, are then continually monitored at all the sensinglocations in the closed cycle. The data is fed into the computer of therecorder-controller 21 where the refrigerant inventory is summed asdescribed above taking into account the set values for the liquidfraction. This data is operated on by the computer continuously or atpreset intervals. The computer output constituting the inventory of therefrigerant in the cycle 20 is printed out by the recorder 39.

Control over refrigerant inventory is maintained by one of three ways.In the first of these methods, a controller is employed. The controllerof the inventory recorder-controller 21 comprises a plurality of devicesresponsive to the computer which are connected to said devices. Thecomputer, continuously or during each preset time interval, compares thetotal molar inventory as well as the total component molar inventory, ifa multicomponent refrigerant is used, with the preset values set intothe program. If one or more of the components are found to be in shortsupply, a signal is sent by means of an electrical conduit such as thatillustrated at 41 in FIG. 2 to one or more of the control valves of thetype illustrated at 36. This opens the valve or valves permitting theflow of one or more components into the system. The signal isdiscontinued when the calculated value for the component comes up to thepreset value. Alternatively, if it is found, and this is much lesslikely to occur, that one or more components are in oversupply in thecycle, a signal is sent to a conduit of the type illustrated at 43 to acontrol valve of the type illustrated at 38 to open the valve and allowthe refrigerant to flow through a conduit 37 to exhaust 40. The signalis discontinued, closing the valve 38, when the calculated quantity ofthe refrigerant component comes within the range of the present value.It should be appreciated that although FIG. 2 illustrates an exhaust ata low pressure suction holdup volume 24, this should not be considered alimiting location for the exhaust system. Thus, exhaust lines may bedisposed throughout the cycle 20. In this way it is possible toselectively exhaust refrigerant rich in one or more components. Forexample, if a multicomponent refrigerant were used and it was found thatsome of the lowest boiling components were in oversupply, a line fromthe top of the high pressure discharge volume 26 could be incommunication with an exhaust line and that line would be opened by thecontroller 21 to discharge the lower boiling components which areobviously in the gaseous phase in volume 26.

The second control method encompasses the employment of the recorder ofthe recorder-controller 21 of the instant invention. Therecorder-controller 21 records the total molar or mass composition ofthe refrigerant. The operator monitors the recorder in conjunction witha chromatograph, and when one or more components is in over or undersupply in the cycle 20, he manually adjusts the valves to input orexhaust any of the components individually. As an example, the operatormight be told to maintain refrigerant component control within 10percent of a preset value.

A third possible method of control entails the combined use of both themanual, or recorder, method of control and the automatic or controllermethod of control. In this method, the system is manually controlledwith an automatic control backup. This method may best be explained byillustration. In a typical operation employing this third method ofcontrol, the operator controls refrigerant inventory within a fixedrange, say 10 percent. At the same time, the controller is preset tofeed or remove refrigerant if the amount of refrigerant varies outsidesome range greater than the fixed range set for manual control, say 25percent. This method may be preferred in some applications because ofits redundancy which therefore provides greater assurance againstfailure.

The embodiment illustrated in FIG. 2, as stated above is illustrative ofany closed cycle refrigeration system. Such a system can be used forexample in a natural gas liquefaction plant where the refrigerant is amulticomponent mixture of C to C hydrocarbons and nitrogen.

It should be understood that the preferred embodiment described above inno way limits the scope of the invention. Thus, it should be understoodthat the apparatus and method of the instant invention may be modifiedwithout departing from the scope and spirit of the invention.

What is claimed is:

l. A process for measuring and controlling refrigerant inventory in amulticomponent refrigeration cycle comprising:

a. sensing the temperature, pressure, and percentage composition of arefrigerant at points in the cycle where said refrigerant is in thegaseous phase;

b. computing the total amount of refrigerant inventory from said sensedtemperature and pressure and an average compressibility factor, theknown amount of refrigerant in the liquid phase; and

c. adjusting the amount of refrigerant in said cycle as a function ofthe variation between a set value for total refrigerant in the cycle andthe amount computed in step (b) and with reference to the percentagecomposition determined in step (a).

2. The process of claim 1 wherein the step of adjusting the amount ofthe refrigerant comprises manually controlling flow into a linecommunicating between a source of refrigerant makeup and the closedcycle, when the total computed amount of refrigerant is more than saidset value.

3. The process of claim 1 wherein the step of adjusting the amount ofrefrigerant in said cycle comprises manually controlling flow from anexhaust line communicating with said closed cycle when the totalcomputed amount of refrigerant is less than said set value.

4. A process for controlling refrigerant inventory in a multicomponentrefrigeration cycle comprising:

a. sensing the temperature, pressure and percentage composition of thegaseous phase of the said multicomponent refrigerant at points in thecycle where said multicomponent refrigerant is held in a constantvolume;

b. computing the total amount of each of said components from theinformation obtained in step (a); and

c. adjusting the amount of each of said components as a function of thevariation of said component between a set value ad the amount computedin step (b) above.

5. The process of claim 4 wherein the step of computing the total amountof each component comprises;

a. determining the total mass of said multicomponent refrigerant in thegaseous phase in each of said points at which the temperature, pressureand composition of the refrigerant in the gaseous phase has been sensed;

b. determining the total mass of each of said components of saidmulticomponent refrigerant in each of said sensing points byapportioning the total mass calculated in step (a) in proportion to thepercentage of each component of said multicomponent refrigerant at eachof said sensed points;

. adding the mass of each component in the vapor phase at all of saidsensing points to yield a gaseous phase total for each component of saidmulticomponent refrigerant; and

d. adding to the totals calculated in step (c) the mass of each of saidcomponents of said multicomponent refrigerant in the liquid phase ateach of said sensing points, whereby the total mass of each component ofsaid multicomponent refrigerant is determined.

6. The process of claim 4 wherein the step of adjusting the amount ofeach component of said refrigerant comprises;

a. comparing the total amount of each component computed with the presetrange for that component;

b. generating a signal to admit additional amounts of said component ifthe value computed is less than the lower limit of said preset range;

0. discontinuing said signal when the amount of said component in thesystem reaches a level within the preset range.

7. The process of claim 6 wherein the step of adjusting the amount ofeach component of said refrigerant is further characterized by the stepscomprising;

a. generating a signal to release refrigerant from a point in said cyclewhere said refrigerant is rich in a component which is computed to beabove the preset range for said component;

b. discontinuing said signal when the total measured amount of saidcomponent reaches a level within the preset range.

8. The process of claim 5 wherein the amount of each of said componentsof said multicomponent refrigerants in the liquid phase is determined onthe basis of controlled fixed liquid levels in each of said sensingpoints.

9. The process of claim 5 wherein the amount of each of said componentsof said multicomponent refrigerant in the liquid phase is determined onthe basis of measured variable liquid levels in each of said sensingpoints.

10. In a closed refrigeration cycle apparatus comprising a refrigerantflowing across at least one compressor with at least one suction holdupvolume upstream and at least one discharge holdup volume downstream ofeach compressor, said cycle characterized by at least one flash valveand at least one heat exchange stage downstream of said valve, saidvalve and said stage disposed between said discharge holdup volume andsaid suction holdup volume, the improvement comprising means for sensingthe temperature, pressure, and composition of said refrigerant in thegaseous phase in each of said suction holdup volumes and said dischargeholdup volumes, means for communicating said sensed temperature,pressure and composition, means for computing the amount of refrigerantin each of said volumes from said temperature, pressure and compositiondata transmitted to said computer means by said communicating means, andmeans responsive to said computer means for adjusting the amount ofrefrigerant in said apparatus.

11. The improved apparatus of claim 10 wherein said sensing meanscomprises a thermocouple, a pressure transducer, and a chromatograph forsensing the temperature, pressure and composition, respectively, of saidmulticomponent refrigerant.

12. The improved apparatus of claim 10 wherein said transmitting meanscomprises electrical conduits communicating said sensed data from saidsensing means to said computing means.

13. The improved apparatus of claim 10 wherein said transmitting meanscomprises pneumatic conduits communicating said sensed data from saidsensing means to said computing means.

14. The improved apparatus of claim 10 wherein said means responsive tosaid computing means comprises a recorder means for recording the massof said multicomponent refrigerant in said cycle, and manual means forchanging the amount of refrigerant in said system so that said amount ofrefrigerant is adjusted within a preset range.

15. The improved apparatus of claim 10 wherein said means responsive tosaid computer means comprises a controller means which controls flowthrough at least one control valve, said valve disposed in an inletconduit communicating between a supply of a single component of saidmulticomsaid control valve disposed in an exhaust conduit communicatingbetween said closed cycle and a point outside said cycle, whereby saidcontroller means opens at least one of said control valves when saidcomputer means indicates an excess of refrigerant.

1. A process for measuring and controlling refrigerant inventory in amulticomponent refrigeration cycle comprising: a. sensing thetemperature, pressure, and percentage composition of a refrigerant atpoints in the cycle where said refrigerant is in the gaseous phase; b.computing the total amount of refrigerant inventory from said sensedtemperature and pressure and an average compressibility factor, theknown amount of refrigerant in the liquid phase; and c. adjusting theamount of refrigerant in said cycle as a function of the variationbetween a set value for total refrigerant in the cycle and the amountcomputed in step (b) and with reference to the percentage compositiondetermined in step (a).
 2. The process of claim 1 wherein the step ofadjusting the amount of the refrigerant comprises manually controllingflow into a line communicating between a source of refrigerant makeupand the closed cycle, when the total computed amount of refrigerant ismore than said set value.
 3. The process of claim 1 wherein the step ofadjusting the amount of refrigerant in said cycle comprises manuallycontrolling flow from an exhaust line communicating with said closedcycle when the total computed amount of refrigerant is less than saidset value.
 4. A process for controlling refrigerant inventory in amulticomponent refrigeration cycle comprising: a. sensing thetemperature, pressure and percentage composition of the gaseous phase ofthe said multicomponent refrigerant at points in the cycle where saidmulticomponent refrigerant is held in a constant volume; b. computingthe total amount of each of said components from the informationobtained in step (a); and c. adjusting the amount of each of saidcomponents as a function of the variation of said component between aset value ad the amount computed in step (b) above.
 5. The process ofclaim 4 wherein the step of computing the total amount of each componentcomprises; a. determining the total mass of said multicomponentrefrigerant in the gaseous phase in each of said points at which thetemperature, pressure and composition of the refrigerant in the gaseousphase has been sensed; b. determining the total mass of each of saidcomponents of said multicomponent refrigerant in each of said sensingpoints by apportioning the total mass calculated in step (a) inproportion to the percentage of each component of said multicomponentrefrigerant at each of said sensed points; c. adding the mass of eachcomponent in the vapor phase at all of said sensing points to yield agaseous phase total for each component of said multicomponentrefrigerant; and d. adding to the totals calculated in step (c) the massof each of said components of said multicomponent refrigerant in theliquid phase at each of said sensing points, whereby the total mass ofeach component of said multicomponent refrigerant is determined.
 6. Theprocess of claim 4 wherein the step of adjusting the amount of eachcomponent of said refrigerant comprises; a. comparing the total amountof each component computed with the preset range for that component; b.generating a signal to admit additional amounts of said component if thevalue computed is less than the lower limit of said preset range; c.discontinuing said signal when the amount of said component in thesystem reaches a level within the preset range.
 7. The process of claim6 wherein the step of adjusting the amount of each component of saidrefrigerant is further characterized by the steps comprising; a.generating a signal to release refrigerant from a point in said cyclewhere said refrigerant is rich in a component which is computed to beabove the preset range for said component; b. discontinuing said signalwhen the total measured amount of said component reaches a level withinthe preset range.
 8. The process of claim 5 wherein the amount of eachof said components of said multicomponent refrigerants in the liquidphase is determined on the basis of controlled fixed liquid levels ineach of said sensing points.
 9. The process of claim 5 wherein theamount of each of said components of said multicomponent refrigerant inthe liquid phase is determined on the basis of measured variable liquidlevels in each of said sensing points.
 10. In a closed refrigerationcycle apparatus comprising a refrigerant flowing across at least onecompressor with at least one suction holdup volume upstream and at leastone discharge holdup volume downstream of each compressor, said cyclecharacterized by at least one flash valve and at least one heat exchangestage downstream of said valve, said valve and said stage disposedbetween said discharge holdup volume and said suction holdup volume, theimprovement comprising means for sensing the temperature, pressure, andcomposition of said refrigerant in the gaseous phase in each of saidsuction holdup volumes and said discharge holdup volumes, means forcommunicating said sensed temperature, pressure and composition, meansfor computing the amount of refrigerant in each of said volumes fromsaid temperature, pressure and composition data transmitted to saidcomputer means by said communicating means, and means responsive to saidcomputer means for adjusting the amount of refrigerant in saidapparatus.
 11. The improved apparatus of claim 10 wherein said sensingmeans comprises a thermocouple, a pressure transducer, and achromatograph for sensing the temperature, pressure and composition,respectively, of said multicomponent refrigerant.
 12. The improvedapparatus of claim 10 wherein said transmitting means compriseselectrical conduits communicating said sensed data from said sensingmeans to said computing means.
 13. The improved apparatus of claim 10wherein said transmitting means comprises pneumatic conduitscommunicating said sensed data from said sensing means to said computingmeans.
 14. The improved apparatus of claim 10 wherein said meansresponsive to said computing means comprises a recorder means forrecording the mass of said multicomponent refrigerant in said cycle, andmanual means for changing the amount of refrigerant in said system sothat said amount of refrigerant is adjusted within a preset range. 15.The improved apparatus of claim 10 wherein said means responsive to saidcomputer means comprises a controller means which controls flow throughat least one control valve, said valve disposed in an inlet conduitcommunicating between a supply of a single component of saidmulticomponent refrigerant and said closed cycle, whereby saidcontroller means opens said valve in said conduit communicating betweena single component and said closed system when said computer meansindicates a shortage of said component.
 16. The improved apparatus ofclaim 10 wherein said means responsive to said computer means comprisesa controller means which controls flow through at least one controlvalve, said control valve disposed in an exhaust conduit communicatingbetween said closed cycle and a point outside said cycle, whereby saidcontroller means opens at least one of said control valves when saidcomputer means indicates an excess of refrigerant.